Phylum Annelida - intestine and accessory glands Excretory...

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Phylum Annelida: Segmented Worms The phylum Annelida contains segmented worms (such a the earthworm, shown in Figure 16). The development of segmented bodies allowed the formation of specialized functions in different segments. Annelids have an enlarged coelom to accommodate more complex internal organs. The well-developed, fluid-filled coelom and the tough integument act as a hydrostatic skeleton . There are about 12,000 marine, freshwater, and terrestrial species usually divided into three taxonomic classes. Similarities of larval forms to Mollusks suggest annelids share an common ancestral group. Annelids have a closed circulatory system with blood vessels running the length of the body and branching into every segment. Closed circulatory systems are more efficient than open ones for moving materials within a body. The annelid nervous system consists of a brain connected to a ventral solid nerve cord, with a ganglion in each segment. Annelids have a complete digestive system that include a pharynx, stomach,
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Unformatted text preview: intestine, and accessory glands. Excretory nephridia in each segment collect waste material from coelom and excrete it through the body wall. The Class Polychaeta Most annelids belonging to the taxonomic class Polychaeta are marine and possess parapodia and setae. Parapodia are paddlelike appendages used in swimming that also serve as respiratory organs. Setae are bristles, attached to parapodia, that help anchor polychaetes to their substratum and also help them move. Clam worms, such as Nereis, are active predators . Many have well-developed cephalization, with a head having well-developed jaws, eyes, and other sense organs. Sedentary filter feeders possess tentacles with cilia to create water currents and to select food particles. Only during breeding do polychaetes have reproductive organs. Polychaet zygotes develop into a type of larva similar to that produced by marine clams....
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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Phylum Annelida - intestine and accessory glands Excretory...

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